PHY101
Chapter Two Review
Newton’s Laws

Study of Newton’s
Laws
Basics of
Force
Newton’s
Laws
Analyzing
Forces
Circular
Motion
Resistive
Forces
Potpourri
$100
$100
$100
$100
$100
$100
$200
$200
$200
$200
$200
$200
$300
$300
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$100
ANSWER

$200
What is the equation for force?
What are the units in the 3 systems?
ANSWER

$300
ANSWER

$400
ANSWER

Newton's Laws $100
ANSWER

Newton's Laws
$200
What is Newton’s First Law?
ANSWER

Newton's Laws
$300
What is Newton’s 2nd Law?
ANSWER

Newton's Laws
$400
ANSWER

Analyzing Forces
$100
What is a free body diagram?
ANSWER

Analyzing Forces
$200
ANSWER

Analyzing Forces
$300
ANSWER

Analyzing Forces
$400
A child stands on a bathroom scale while riding in an elevator. The child's weight when the elevator is not moving is 200 N.
What is the child’s mass in kg?
What does the scale read (tension T) when the elevator accelerates upward at 1.00 m/s 2 ?
ANSWER

Circular Motion
$100
If an object moves in a circle, what kind of force acts the centripetal force?
ANSWER

Circular Motion
$200
What is the equation for centripetal (radial) force?
ANSWER

Circular Motion
$300
What is Newton’s Law of Gravity?
ANSWER

Circular Motion
$400
What is the acceleration due to the earth's gravity at a distance of one earth radius above the earth's surface?
a. 2.5 m/s² b. 5 m/s² c. 10 m/s² d. 20 m/s²
ANSWER

ANSWER

ANSWER

ANSWER

A horizontal force of 640 N is applied to a car with a mass of 1600 kg. What is the acceleration of the car if the coefficient of rolling friction is 0.01?
a. 0.02 m/s² b. 0.03 m/s² c. 0.2 m/s² d. 0.3 m/s²
ANSWER

Potpourri $100
A 9.00-kg object is moving in a circle with a constant speed of 45.0 m/s.
If the circular path has a radius of 20.0 m, what is the net force on the object?
ANSWER

Potpourri $200
What are the conditions for simple harmonic motion?
ANSWER

Potpourri $300
Before going to the beach, you check the position of the moon. Why?
ANSWER

Potpourri $400
The average orbital speed of Mars is 2.41 x 10 4 m/s.
If the radius of Mars's orbit is 2.28 x 10 11 m, how long does it take Mars to complete one orbit?
ANSWER

Basics of Force
$100
Answer
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Basics of Force
$200
Answer
What is the equation for force?
Force = F = ma = m D v / D t
SI unit 1 kg*m/s² = 1 Newton = 1 N cgs unit 1 g*cm/s² = 1 dyne
Common unit 1 slug*ft/s² = 1 lb.
1 N = 10 5 dynes = 0.2248 lbs
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Basics of Force
$300
Answer
What is weight?
Weight is the force of gravity acting on a body.
W = mg where g is local gravity
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Basics of Force
$400
Answer
What is momentum?
Momentum is mass X velocity p = mv Unit is 1 kg*m/s in SI
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What is mass?
Mass is a measure of an object’s resistance to acceleration. It is a measure of the quantity of matter in an object.
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What is Newton’s First Law?
An object will remain at rest or in motion with a constant velocity unless acted upon by an outside force.
 F = 0 v = constant a = 0
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What is Newton’s 2nd Law?
An object is accelerated whenever a net external force acts on it. The net force equals the objects mass times its acceleration.
 F = ma
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What is Newton’s 3rd Law?
Forces always come in pairs. When one object exerts a force on a second object, the second exerts an equal and opposite force on the first.
 F = 0 F
12
= -F
21
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Analyzing Forces
$100
Answer
What is a free body diagram?
A free body diagram is a force picture showing all the forces, the net acceleration and the direction of motion.
 F y
= ma = T - mg T a
T = mg + ma
T = m(g + a) mg
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Analyzing Forces
$200
Answer
What is a normal force?
A normal force is a (reactive) balancing force such that  F = 0.
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Analyzing Forces
$300
Answer
What is Hooke’s Law?
This is a conservative spring force equation.
 F= - k
S x = ma where k
S
= Weight of spring & object/stretch in SI units of N/m
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Analyzing Forces $400
Answer
A child stands on a bathroom scale while riding in an elevator.
The child's weight when the elevator is not moving is 200 N.
What is the child’s mass in kg? m = Weight/g = 20.4 kg
What does the scale read (tension T) when the elevator accelerates upward at 1.00 m/s 2
?
 Fy= ma = T - mg
T = mg + ma
T = m(g + a) = 220 N
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Circular Motion $100
Answer
If an object moves in a circle, what kind of force acts the centripetal force?
A real force like tension or gravity must act as a centripetal force and point toward the center of the circle.
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Circular Motion $200
Answer
What is the equation for centripetal (radial) force?
 F centripetal
= mv²/r
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Circular Motion $300
Answer
What is Newton’s Law of Gravity?
F = G m
1
*m
2
/d²
G = 6.67 * 10 -11 N*m²/kg²
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Circular Motion $400
Answer
What is the acceleration due to the earth's gravity at a distance of one earth radius above the earth's surface?
a. 2.5 m/s² b. 5 m/s² c. 10 m/s² d. 20 m/s²
F = G M*m/d² = mg
If d new
= 2d, then F
NEW
= G M*m/(4d²) = mg
NEW
= mg/4 g
NEW
= g/4 = 2.45 m/s²
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Resistive Forces $100
Answer
What is a drag force?
A resistive force called air resistance.
Drag Force = ½ C*density*Area*v²
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Resistive Forces $200
Answer
What is friction?
A force of resistance to relative motion between 2 bodies or substances in physical contact.
f = Coefficient of friction *Normal Force = µF
N
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Resistive Forces $300
Answer
Name two types of friction?
Static friction no motion
Kinetic friction motion
10
5
0
25
20
15
40
35
30
0 10 20 30 40
Pull in N
50 60 70 80
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Resistive Forces $400
Answer
A horizontal force of 640 N is applied to a car with a mass of 1600 kg.
What is the acceleration of the car if the coefficient of rolling friction is 0.01?
a. 0.02 m/s² b. 0.03 m/s² c. 0.2 m/s² d. 0.3 m/s²
 F y
= 0 = F
N
– mg F
N
= mg = 15680 N f
K
= µF
N
= µmg = 157 N
 F
X
= ma = Pull – f k
= 640 N – 157 N = 483 N a =  F
X
/m = 483 N/ 1600 kg = 0.30 m/s²
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Potpourri $100
Answer
A 9.00-kg object is moving in a circle with a constant speed of 45.0 m/s.
If the circular path has a radius of 20.0 m, what is the net force on the object?
F = mv²/r = (9.00kg)*(45 m/s)²/(20.0m) = 911 N
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Potpourri $200
Answer
What are the conditions for simple harmonic motion?
1. Motion must be periodic
2. Force must cause the motion and be parallel to it.
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Potpourri $300
Answer
Before going to the beach, you check the position of the moon. Why?
Low tide = moon on horizon
High tide = high point in sky
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Potpourri $400
Answer
The average orbital speed of Mars is 2.41 x 10 4 m/s.
If the radius of Mars's orbit is 2.28 x 10 11 m, how long does it take Mars to complete one orbit?
V = 2 p r/T
T = 2 p r/v = 5.94 * 10 7 sec = 688 days
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